Add 6mm square adapter plus openscad project

Add adapter for 6mm square tilt rod, together with the scad file to
create it in case it is useful for creating other variants.

Signed-off-by: Matt Redfearn <matt.redfearn@gmail.com>

BlindsAdapter.scad

@@ -0,0 +1,17 @@
+
+
+$fn=144;
+
+shaft_diameter = 6.5;
+
+difference() {
+    cylinder(18, 7, 7);
+    
+    //Blinds shaft
+    translate([-shaft_diameter/2, -shaft_diameter/2, 7])
+        cube([shaft_diameter, shaft_diameter, 11]);
+    
+    // Motor shaft
+    translate([-6/2, -3.5/2, 0])
+        cube([6, 3.5, 7]);
+};